Shock-absorbing strut



Patented June 24, 1930 UNITED STATES PAT-ENT vori-lolz JOHN F. WALLACE, OF SHAKER HEIGHTS," OHIO, ASSIGNOR T0 THE CLEVELAND PNEU- MATIC TOOL COMPANY, 0F CLEVELAND, OHIO, A' CORPORATION 0F OHIO SHOCK-Ansonnme sTnUT Application filed December 9, 1927. Serial No. 238,838.

This invention relates to improvements in shock-absorbing struts for use primarily in the landing gears of airplanes and hydroplanes.

One of the objects of the invention is the provision of a strut which is of relatively compact, simple construction and whichmot only takes the impact of landing and other blows delivered to the landing gear as the plane moves over the ground or water but also absorbs the rebound resulting from the compression ofthe compressible Huid in the strut.

More particularly, 'it is the aim of the in vention to provide a strut composedof telescoping members having on the interior a chamber in which oil or othernon-compressible iiuid and compressed airareY contained, with provision whereby when the impact occurs in landing a very satisfactory cushioning action is obtained, with equally satisfactory provision for preventing sudden rebound. That is to say, the return movement of the telescopic members is retarded so as to be relatively slow as compared with the telescopic movement in the op )osite direction.

nother object is the provision in apparatus of this character of a verysimple, oneway valve of low cost and great reliability. Still another object is an arrangement of parts by. virtue of which the pressure exist- Ving below the piston incident to the rebound stroke is utilized to effect a heavy frictional contact of the packing employed to seal the relatively sliding parts, thereby not only effectively preventing the loss of pressure fluid at a time when such loss is quite liable to occur but also adding toA the resistance available toV oppose the rebound stroke, and making the action of the device exceptionally smooth.

, Other objects and features of novelty will appear as I proceed with the description of that embodiment of the invention which,

for the purposes of the present application,

I have illustrated in drawings, in which:

Fig. 1 is a longitudinal sectional view of a strut embodying the invention;

the accompanying Fig. 2 is a transverse section taken sub stantially on the line 2 2, Fig. 1;

Fig. 3 is a transverse section takensubstantially on the line 3-3, Fig. 1; and y Fig. 4 is a cross-section taken substantially on the line 4.-#4, Fig. 2, showing the piston on a larger scale and showing the valve ring in a position different from that illustrated in Fig. 1.

In the drawing, there are 'illustrated two principal telescoping parts. The upper and outer one maybe referred to generally as a cylinder 10, and comprises a tubular member 11 threaded at its upper end to receive a dome-shaped head 12.' The lower end of the tubular member 1l is enlarged, as shown at 13, to accommodate theppackingwhich will be described presently.' 1

Within the tubular member 11 there is positioned a metal piston 14 finished to a nice sliding fit and preferably provided with a plurality of circumferential oil grooves'l. A piston rod 16, of a diameter smaller than that of the piston, and preferably tubular in form, is connected to the piston in some suitable manner. To this end, I may form the piston 14 with a shank 17 which is threaded into the threaded upper end of the tubular piston rod 16, thereby connecting the two together rigidly.

Any suitable means may be provided for attaching the cylinder 10 and the piston rod 16 to such relatively movable parts of a vehicle as it may be desired to cushion. AThese connections willlv'ary considerably with the type of vehicle-t0 which the device may be applied. For use upon airplanes, I may attach to the head 12 by a threaded joint a tubular extension bar -18 and at the free end of .the latter I` may attach by a threaded joint or the like a connector 19 having a 'perforation20 for the reception of an attaching bolt or pin. The lower end of the tubular piston rod 16 may be threaded to receive a reducing connection 21 to which is threaded a tubular extension bar 22 simi- -lar to the bar 18, and it will be understood that at the free end of this bar 22 thre may be attached any suitable connector, aS`,

for instanace, a duplicate of the connecten The cylinder 10 is to be filled with fluid, preferabl oil and air under pressure. Any suitable lling plugrand valve may be used, and as its construction forms no part of the present invention, I have shown merely the external outline of such a plug at 23.V

A flat metal ring 24`is loosely mounted upon the smooth up r portion of the shank 17 of the piston, t 's ring being movable within a recess 25 formed between the piston proper and the upper end of the tubular piston rod 16. The ring 24 has ports 26 extending therethrough at equal distances from the center of the ring. At the same radial distance the piston 14 is also provided with one or more passages 27 extending parallel to the axis of the cylinder 10, and these passages, if desired, may have restrictions 28 therein. The lower surface of the piston head, or the upper surface of the ring 24, or both, may be provided with a,l circular groove in order to insure an uninterrupted ow of'tluid through the passages 27 and ports 26 when the valve ring 24 is in its upper position against the head of the piston. In the present instance, I have indicated such a groove at 29 on the under 'surface of the piston and another'such groove at 30 on the upper surface of the ring. 24. A second series of passages 31 'extend through the piston 14 from its upper surface to the recess'25l but at a shorter radial distance from the center of the piston where 1 they are covered by the upper flat surface of the valve ring 24 when' the latter is in its upper position.

An annular shoulder 32 is' formed at the juncture between the tubular member 11 and its enlargement 13. VAn annular retainer 33 is mounted to slide between the 'surfaces of the piston rod 16 and the enlargement 13, its movement in one direction being limited by the shoulder 32 which thus acts as a stop. Below the retainer 33 and inthe annular space between the cylinder enlargement 13 and the piston rod 16 is located packing 34 which is in the form of rings, some of ,which are made up in such a way that they expand radially when preure is exerted u n them in a direction parallel to the axis of the cylinder. In the end ofthe enlar ment 13 there is threaded a gland nut 35 w eh bears upon the lower end ofthe packing 34. Q This Y nut 35 is employed t'o control the friction exerted upon the walls of the parts 16 and 13 by the acking As this nut is threaded mwar y, the packing 34 is expanded and the friction correspondingly increased. The lock ring 36 is employed to hold the nut 35 in an given adjusted position. The packing 34irs a known commerci article and its detailed make-up forms no part of the present invention.

After the parts are assembled and the strut is mounted for instance, between the landing gear and the frame of an airplane the filling plug 23 being open and the cylinder and piston in their collapsed position, that is, with the piston up to the head of the cylinder .or approximately, so, oil is introduced until the head 12 is practically' filled. Then an air pressure hose is attached to the iilling plug 23 and the strut is inflated until the weight of that side of the airplane is balanced by the air pressure within the strut with the piston in substantially the position shown in Fig. 1. During this ination the cylinder 10 obviously rises, lifting the airplane. At this time oil fills the annular space 9 between the piston 14 and thef packing retainer 33 and stands somewhat above the top of the piston.

Now, when the airplane rises from the ground and the weight is taken off the strut, the pressure in the cylinder 10 ex ands the strut to the limit, that is, until t e piston 14 engages the retainer 33 and presses upon the same with all of the pressure available upon the top surface of the piston. By this means the ring 33 is depressed, expanding they,paeking 34 considerably. A very tight seal is thus formed between the two telescoping members 10 and 16 when the plane is in the air. Hence, none of the oil which is in the lower endof the strut leaks out, and if the airplane is inverted in flight, as

sometimes occurs, yso that air under pressureV impinges upon the packing, the seal is still tight enough to prevent any apv reciable loss of pressure, which is a high y important `result in devices of this character.

When a landing is made, the landing gear strikes the found with considerable force.

This force causes the piston 14 to move rapidly upward in the cylinder 10 against the compressed air therein contained. lAt the beginning of this stroke, the oil in the strut is practically all above the piston;- However, the ring 24 is in its lower position, as shown in Fig. 1, and a minimum resistance is offered to the How-of oil through passages 31 and 27 into the recess 25 and thence through ports 26 into. the annular As soon as the piston moves`awa from the retainer p33 and advances rapid y into the cylinder 10, thereby greatly reducing the. area through which the pressure in the cyl. inder 10 may act uponthe retainerr33, and thereby creating'a light vacuum in the annular spacev below the piston head, pressure upon the retainer 33 is greatly relieved and it moves upwardly into engagement with the shoulder 32, therebyv ysubjecting the sliding parts to the minimumgof friction from spaces below the piston.

al the packing 34.

,When the force of the impact 1s balanced by'the pressure built up above the piston,

the latter stops and the energy thus stored up in the highly compressed air in the cylinder Vtends to' drive the piston downwardly with a lviolentv motion. The piston head immediately catches up with the loosevalve ring 24, as indicatedqin Fig. 4, and the latter is held in its uppergposition by the pressure of the oil beneath.1 'Conse-.i

quently, the passages 31 are closed and the -oil can flow upwardly past the piston onlyf so fast asA it can be metered through the restrictions .28 in the passages'27. The rebound is thus slowed up. At the same time,

however', the oil in the annular space. 9 transmits the heavy pressure above the piston down upon the retainer 3,3, forcing the same downwardly and expanding the v'packing 34. By this means heavy friction lbetween the sliding parts is added to cntribute to the 'slowing up of the rebound stroke,4 p l A While, as previously stated, this invention is intended primaril for use in air- A planes and hydroplanes, do not desire .to restrict the invention 'in this respect, as it .is capable vof application to other vehicles, as Kor instanceautomobiles.

Having thus described my invention, I

s claim:

1. In a shock-absorbing strut, a cylinder, a member telescoping therewith, a piston on the. inner end of said member iin slid ing engagement with the cylinder, expanvsible packing between said cylinder 'and telescoping member exposed to the pressure of the fluid surrounding said memberbe` hind said piston, and means for permitting the flow of fluid from one side of the piston to the other more freely in one direction than 1n the other, wherebythe fluid between said piston and said paclng serves not only as a rebound check but also as means for regulating the friction between said packing and the adjacent parts.

2. In a shock-absorbing strut, a cylinder, a member` telescoping therewith, 'a plston on the inner end of said member in sliding Vengagement with the cylinder, expansible packing between-)said cylinder and telesco in member exposed to the pressure of the ui surrounding saidl member behind said pitston, and means for permitting the flow of fluid from one side of the piston to the other comprising a one-way valve, where- 4by( the luid between said piston and, said acking serves not only as a rebound check ut also as means for regulating. the frict1on betweenl said packing and the adjacent parts.

3. In a shock-absorbing strut,'a cylinder,

a member telescoping therewith, a plston on the inner end of saidmember in sliding engagement with the c linder, expansible packing between said 'cy der and telesco ing member exposedy to the p of t e tolrnove therein longitudinally of the pistqil a port therethrough `at a distance line with said annular iluid surrounding said member behind said piston, said piston having a passage therethroughronnecting the s ace between the) piston and cylinder 'hea .with the .space below the piston outside said. telescoping member, and a valve carried by said piston' 'recess intersecting said passage, and a ring mounted loosely in said recess and adapted as the direction of movement thereo changes, said ring being adapted torcover said` passage in one position and open it 1n the other.

5. In a shock-absorbin strut, a cylinder adapted to hold fluid un er pressure, a piston therefor, said cylinder providing chambers upon-both sides of said pisstonyvheny the latter `is in an intermediate posltion,

'said piston-having a passage therethrough connecting. said chambers, said piston also having an annular peripheral -rece inter; secting said passage,. and afringloosely mounted in said recess. constituting a valve for opening and'closing said passa e as the piston moves in one direction or; t e other,

'whereby movement of the piston is restricted in one direction more than in the 6. In aLshock-absorb' strut, a cylinder adapted to hold fluid un er pressure; a piston therefor, said c linder providing chambers upon both4` si es of said piston when the latter is in an intermediate position,

said piston also having an annular. recess intersecting said passage, and a ring loosely mounted in Vsaidreeess provided with from the center radially equal to that of said pas, sage, there beingsan annular groove in-one of the adjacent surfaces of said piston and' ring, whereby the flow -of fluid through said passage and rt is not aifected by their relative relation, said piston -having a second paage therethrough intersecting said annular r at a point out of ve. In testimony'whereof, hereunto ailix my signature. Y Y Y g JOHN F. WALLACE.,

said piston having a passage therethrough, lfloi 

